


Blue Screened

by ActuallyFace



Category: Undertale (Video Game)
Genre: Angst, Babybones, Child Neglect, Core Accident, Multi, Nightmares, Nonverbal Communication, Nonverbal Gaster, Sign Language, Skeleton family
Language: English
Status: In-Progress
Published: 2015-12-08
Updated: 2015-12-29
Packaged: 2018-05-05 14:45:42
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 9
Words: 8,126
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5378996
Author URL: https://archiveofourown.org/users/ActuallyFace/pseuds/ActuallyFace
Summary: <blockquote class="userstuff">
              <p>Sans is unusual, it's Gaster's fault, and the rest of the "core accident" story.</p>
            </blockquote>





	1. Warmth

Sans was laughing, his voice ringing high and clear across the snowy landscape. It came back to mingle with the more nasally sound of his brother’s frustrated puffs and protests, far behind Sans but growing nearer. While Papyrus’ tiny footprints carried on in a long, hectic line from one end of Snowdin to the other, Sans’ only seemed to appear in a couple of places, with long pauses in between them.

“Sans!” Papyrus called, “This is cheating! You cannot win by cheating!” 

“Looks like I already am, bro.” Sans taunted, grinning as his brother approached and then barreled past him. Papyrus blew out another frustrated huff in response. Sans’ grin widened, and he turned, disappearing through the door of the shop behind him. 

He reappeared another thirty feet ahead, and when Papyrus yelled wordlessly in reply, Sans buckled over with laughter. 

The two raced their way to Grillby’s in similar fashion, Sans disappearing whenever Papyrus caught up to him, then reappearing again just far enough ahead that he had time to tease the other before he was passed again. In the end, he let Papyrus win by a slim margin, and strolled casually through the front door of Grillby’s house behind his huffing and puffing brother.

Grillby was seated on a large, puffy-looking couch in his living room, reading a novel-- somehow. When Sans and Papyrus burst through his door, though, he stood and strode over to greet them. His hands flickered through a series of signs; the one for “hello”, and the individualized motions Gaster had assigned Sans and Papyrus when they were young. Gaster had taught them both sign language, but the brothers responded verbally instead, and Grillby gathered them into a warm hug. When he finally let go, both boys were giggling again, and complied excitedly when Grillby motioned them into his kitchen.

The whole house exuded a warmth similar to the natural one Grillby held, through chocolatey browns, deep reds, gold-like yellows, and oranges that invoked sunsets. The kitchen was no different; not exactly stylish, not exactly new, or big, or expensive, but rather small and cozy. It was just enough, no more and no less.

Sans and Papyrus clambered onto the stools that sat on the other side of the kitchen’s island, and Grillby began to move around the kitchen in a familiar pattern. 

“Yesterday, Sans and I went to Waterfall.” Papyrus announced proudly, “We brought the bird some bread and let it carry us over the gap and back!”

“You let it carry you back.” Sans corrected, “It was too tired by the time it got to me again.”

“But you got home! How else would you get home?”

“Don’t worry about it.” Sans replied hastily, realizing his mistake.

“Sans!” 

“We saw the echo flowers before that too, Grillby.” Sans told the man, changing the subject. Papyrus didn’t seem to notice.

“Yes! And the stones in the ceiling, it was beautiful!”

Grillby walked back to the two and set down a couple of plates in front of them; ketchup sandwiches. Their favorite.

“Thanks, grillby.” Sans grinned at him and began to eat.

“Sans! You embarrass him with your subpar graciousness! These, Dad- um, Grillby, are... true works of art. Masterpieces!” If Papyrus had blood and skin, he would be blushing. 

Grillby seemed to smile, patted Papyrus on the head, and sat down on Sans’ other side. This was evidently something he was used to happening, and he didn’t seem phased. Papyrus continued to jabber on about the previous day, about the wistful stories the echo flowers told, and the strange ghosts that ran the snail farm. He told them about how he and sans had raced the snails, and he had won. Sans was mostly silent, listening to his brother’s cheerful narrative. 

When Papyrus diverged from the part of the day he and Sans had spent together, Sans tried to focus on his sandwich. Papyrus had friends in Snowdin, and while Sans didn’t exactly mind that, he knew he wouldn’t be able to really share those friends. Kids didn’t like those that were different from them. They didn’t like Sans.

Finally, long after both of them had finished, Papyrus hopped down from his stool and scampered off to the living room. Grillby kept action figures and things there for Papyrus to entertain himself with, and Papyrus gladly did so.

The conversation lulled. Silence fell. 

Neither of them minded this. It wasn’t a sour sort of silence; it felt peaceful, the two sharing a space and moment together without the need for words.

After a little while, Sans sighed and rested his head on his arms. The joyful air about him faded, replaced by a tiredness that didn’t suit his years… and soon enough, the tiredness shifted into a quiet melancholy, and Sans lost himself in thought. 

His eyes dimmed, and Grillby was alone in his peaceful moment. 

When Sans’ mood shifted again into something more actively upset, Grillby turned to him, and placed a fatherly hand on the boy’s shoulder. 

“I think dad is doing something” Sans mumbled, but his words didn’t seem entirely directional; they drifted from his mouth like Sans was only letting them. “Planning something, I mean, he spends a lot of time in the lab. More than he usually does. I had a nightmare last night that he didn’t exist.” 

Grillby’s hand tightened on his shoulder, squeezed.

“My nightmares are getting worse. Dad won’t talk to me about them.” He sighed, “And Paps can tell dad’s getting… different. Not different, just less of himself. Paps takes the brunt of it when dad starts acting less.... there. He plays with his friends more during the day, because they distract him. He takes care of me, and he… he doesn’t want to have to all the time, so I leave him alone. His friends won’t play with me anyway.”

The silence returned, and this time it was hollow and hard. Grillby shifted in his seat, facing Sans a little better.

“You are never alone so long as some still love you.” Grillby’s rare string of verbality came out quiet, low, and filled with comfort. “Some do still love you.”

Sans’ eyes flickered over Grillby’s featureless face for a moment, wide and filled with emotion, before he slid over into Grillby’s lap and began to cry.


	2. Frigidity

**Summary for the Chapter:**

> Sans has a nightmare, and Papyrus succeeds where Gaster can't.

**Notes for the Chapter:**

> TW: Nightmares, neglect, knives, suffocation.
> 
> Listen, I know it's angsty, I swear it'll get less melodramatic eventually.

The fear, the anguish, and the miserable rage were more prominent than the actual images in Sans’ mind. He felt them deep and sharp, driven deeper by what he saw; a knife, dusted skin, and sweaty bangs a thin veil over gleaming red eyes. 

When he woke, the feelings followed him out of his dream. They leaked from his sockets and constricted around his airway and his soul with a shaky and damp grip. Sans gasped and sputtered and clenched a hand in the fabric around his ribcage, trying to breath, trying to find air, trying to calm his mind and his heart.

When sobs began to break through the gasps, Sans heard a shifting in the room beside his.

“Sans?” It was Papyrus, groggy and freshly woken, with a voice too full of comfort and concern for one so young. He stood in Sans’ doorway only for a beat, then rushed in to gather his mess of a brother into his arms.   
Sans curled into him.

This was a familiar thing for them both, but that didn’t remove the emotional impact. The brothers clung to each other, Sans shaking and Papyrus rocking, riding out the storm together in a rickety boat of their own design. Sans was tense, stiff, squeezing his fingers and grabbing Papyrus with all the strength he possessed, and Papyrus melted forward and around his brother, trying to protect him, to shield him physically from the emotional turmoil within; a helpless, futile thing. To Sans, though, an important one.

It was a long time before Sans was calm again. And slowly, he pulled himself from Papyrus, who cautiously (but with great relief) returned to bed. 

Finding sleep impossible, Sans wandered downstairs to the living room. He stood there for a moment, feeling unsteady and aimless, until he heard sounds of activity permeating the heavy stillness from the back of the house; the lab. He followed it. 

“Dad?” He mumbled warily from the doorway, and Gaster gestured briefly to show that he was aware of Sans’ presence. The man was crouched, facing away from Sans, and unwilling to look up at him; Sans understood. He was working on his Machine, and that was important. Sans moved inside and closed the door, blinking and squinting in the bright light.

“I had a nightmare.” Sans’ voice was quiet, unsure; lacking the confidence to speak much louder than a whisper, to take up too much space or attention. After a moment or two with no response, Sans worked up the strength (or perhaps desperation) to speak again; “There was a knife, and dust, and… this person with red eyes, and…” he trailed off, uncertain again. Gaster still wasn’t responding. He fell silent.

“I think it was real.” His voice rose, shook, tumbled out impulsively. “I died. I think I’m going to die. It keeps happening, I think Paps dies, it’s getting worse, dad, I don’t know… what’s happening. What to do.” He was near tears again, so he stopped. He didn’t like crying in front of Gaster. 

Gaster’s eyes flicked over to him, and a hand shaped the word “Sorry”; and then he was focused on the Machine again. 

Sans stared at him, tense, caught between a need for emotional relief and comfort, and the knowledge that Gaster didn’t care, that it didn’t really matter.

Again, he spoke.

“I think I’m different. I think I’m bad.”

That gave Gaster pause; he turned from his work, stood, and moved close to Sans. His hands moved again; “You are different. That’s what makes you better.”

Sans stared in disbelief; better? That didn’t make sense, and the fact that Gaster thought it might be comforting made it worse. Sans didn’t want to be better, because even better was different. He wanted to be the same. Without nightmares, abilities, strength no one else had. He wanted friends. 

Better wasn’t comfort, it was pain. It was worse. It was loneliness.

When his expression fell and turned to tears, Gaster only appeared interested; and that was the final straw. Sans turned from him and ran inside. Back upstairs; to Papyrus, to someone who cared and held him while he cried for the third time that day.


	3. Locked Out

“The 13 Wrench, Sans.” The words flickered through Gaster’s fingers, and Sans filled them with the appropriate tool. Gaster did something small to The Machine with it, then handed the tool back and demanded another. When he moved, Sans moved; when he spoke, Sans did as he was told.

 

It was a Lab Day, which wasn’t necessarily _fun_ , but which Sans didn’t mind anyway. It was time with his father, and it was quiet, alone, almost entirely still. The tasks were easy and mind-numbing, which left time for Sans to think.

 

Think… about The Machine, and what it might do. Gaster had been working on it for a long time, for as long as Sans could remember, and Sans had never managed to gather much information about it. It was important, he knew, and supposedly it was intended for the King. Well, not supposedly; Sans had met Asgore a few times, when he’d visited to talk to Gaster about the Machine and the progress that was being made. It was going to change the world, It was the thing upon which the fate of monsterkind depended, it was the center of everything in the Underground. Somehow.

 

He didn’t know what it did. Gaster didn’t ever tell him, and Sans couldn’t read his father’s writing; it was all in some special code he’d invented, one Sans was sure he’d never learn. To protect it, he guessed. Keep it from being known and misused.

 

Gaster’s hand brushed Sans’s when he handed back a socket wrench, and Sans stared for a moment, almost shocked by the sensation. When was the last time Gaster had held him? It had been a while.

 

He put the socket wrench away, and handed his dad a screwdriver and a strangely-bent piece of metal.

 

“Dad?” He chanced. Gaster didn’t respond, so he continued; “What does it do?”

 

His dad paused, looked at him.

 

“The machine. I was just wondering because you never told me.”

 

Gaster’s mouth twitched, forming the beginnings of a smile. His fingers pressed the objects they held to the ground, and moved; “It does great things. It makes monsters better and stronger, and it will make King Asgore a God someday.”

 

Sans frowned a bit, furrowed his brow. The optimism on his father’s face was rare, and he wasn’t sure how much he believed it, or his words. They felt frail, insubstantial, like they weren’t really the whole truth. What Gaster described was magic, and he knew his father didn’t possess magic. Science was different. It didn’t work that way; Sans paid enough attention to know that.

 

But he let it go; his dad turned back to his work, and the moment fell away.

 

* * *

 

 

Gaster ended the workday with a satisfied clap, which whistled as the air rushed through the holes in his palms. The two emerged from the Lab together, and Gaster settled himself into the couch. Unsure what else to do (and urgent for more time with his father), Sans took the seat beside him; not quite touching, but close. Gaster paid him no mind, instead picking up and fiddling with an oddly-shaped, complex-looking object beside the couch.

 

He did this often, as a sort of thinking exercise; took things apart, put them back together, his long fingers moving with the speed and grace of dancing spiders.

 

Sans watched him, silently observing his movements and his actions. Gaster was his teacher, and often that more than anything else. Sans valued the bits of knowledge he dispensed. They were like gifts to him, things he could hold onto when he despaired the lack of something more tender.

 

After a long while of this, Gaster set the object aside and faced Sans.

 

“You are different.” He started, his features bearing a pride-filled smile. Sans stared, already unsure how to react tot he direction his Father was taking. “This is good, because it means you have something more that others do not. You have power that others cannot possess.” Sans remained silent, his stare hardening. Gaster sensed dangerous ground and decided to shift the topic a bit.

 

“You can teleport.” Sans nodded vague confirmation. “How far? How quickly? How has this changed since last month?”

 

“I don’t understand.” Sans replied, fidgeting with the edge of his jacket. “It’s, uh… I can do more, I think, if that’s what you mean. When I use it, I can do more with it.”

 

Gaster nodded. “But how much more? A substantial amount?”

 

“I, uh… since last month, not really. Just a little. It’s getting easier, too, but it doesn’t grow that fast.” He paused, frowning. “Why’s it that important?”

 

“Because if it grows, it can grow more. It can become more. Perhaps, when you grow older… things will settle down within you, and the dreams will straighten themselves out. You do dream?”

 

Sans nodded.

 

“But it is erratic, uncontrolled. There is a chance that you will gain the ability to control it someday, as you have gained the ability to control your teleportation and telekinetic abilities.” He sounded as if he was thinking out loud, more than trying to hold a conversation.

 

“I don’t get what you’re trying to say. Is this some kind of data collection? What does this have to do with anything?”

 

“It… is data collection, of a sort. It is relevant to the Machine, but not in a way that you are ready to understand.”

 

“Why are you telling me anything, then?”

 

Gaster sighed, and the sound was sort of hollow. “We can drop this, then, for now. I suppose I can gather information when you are ready to give it.” Now he looked frustrated, and his movements grew tighter and more jerky. Sans opened his mouth to respond, suddenly wounded; he’d felt pride from his father, for a moment; why was he reacting so badly? He should be enjoying this, soaking it in-

 

Papyrus burst through the door, bringing with him the fresh chill of snowy air. “Brother! Father! I have had the most extraordinary day!” 

 

Gaster fell silent, and Sans turned his attention to his brother.

 

“You have a lot of ‘most extraordinary’ days, Paps.” Sans teased, his mood already rising.

 

“Yes, but this one is _truly_ the most extraordinary! Sans, I have found a new friend! She is blue, and very strong, and she lives near the snail farm!”

 

Sans grinned. “Sounds exhilarating.”

 

“Yes, you understand! Her name is Undyne, and I think you will like her. Maybe you will become friends!”

 

“Maybe.”

 

“Do not be so gloomy, Sans. Be sure! Like me! I _know_ you will enjoy her. And Father! Maybe she can help you, she is very strong!”

 

Gaster looked up and stared at Papyrus, stared… through him. His expression was blank, his pride and his smile gone. He didn’t respond. When Papyrus realized his mistake, he switched smoothly back to talking only to Sans; he barely missed a beat, as if he’d done this before.

 

Sans noticed.

 

“I met her when I visited the Bird today. She is very enthusiastic about the Bird, and was feeding it something. I think it was some kind of clam, and I am not sure the Bird knew how to eat this food, but it appreciated her kind gesture. I think they are good friends!”

 

“Of course; birds love blue monsters, it’s common knowledge.”

 

“Do they? How splendid! Perhaps that it why it is so kind to you, Sans. We should bring it something blue, as a gesture of appreciation.”

  
  
“Oh, absolutely.”

 

“Would you help me find something blue tomorrow, Sans? Perhaps one of your jackets, something to keep it-”

 

Gaster stood suddenly, appearing angry. Without making eye contact, he left the room.

 

Papyrus paused, looked after him for a moment; then kept talking.

 

Sans dropped the banter, and stared after his father. His demeanor became distant, then angry. Papyrus fell silent and watched him.

 

Sans turned his gaze back to Papyrus, who now looked worried and sort of afraid, and felt a pang of guilt. “Papyrus, I’m sorry-- what were you saying?”

  
Papyrus found his grin again, and continued. Without much success, Sans attempted to mimic his former cheerful attitude.

 

* * *

 

“Dad.”

 

Sans stood in the doorway of his father’s room, posture stiff and strong. Gaster turned to look at him.

 

“You ignored Papyrus. You just- you ignored him. Why did you ignore him?”

 

Gaster stared, unresponsive.

  
  
“He _needs_ you! You’re his dad, you’re _our_ dad!”

  
  
“He is happy, is he not?”

 

“You can see. You know it’s hard for him!”

 

“But he is happy.”

 

“Not as happy as if you would listen to him.”

 

“I do not need to listen to pointless jabbering, Sans. He knows that.”

 

Sans clenched his fists and glared at the man, all but shaking. The anger had come on quick, and he was having trouble holding onto it. Gaster, however, was entirely calm. “But it’s not pointless, it’s…”

 

“It has no bearing on anything. It is nothing. It is simple and surface-level, and Papyrus understands that there are more important matters I have promised my time to.”

 

“How can you just-”

 

“Sans, this is pointless, and it will solve nothing. There is nothing to be solved. Your anger is directionless.”

 

Sans gaped.

 

“Will you leave me to my matters, now?”

 

“... I guess I will.”

 

As he left the room, still tense, still clearly upset, Sans noticed Papyrus sitting at the top step of the stairs that ended just outside Gaster’s room. He thought his brother appeared… small, for a moment; concerned, and guilty.

 

“Paps, hey.”

 

Papyrus turned, and his eyes brightened. “Sans! I wanted to-”

 

Sans cut him off; “You’re a great brother, you know.” He grinned at Papyrus. “The best. You’re the best bro a bro could have.”

 

Slowly, Papyrus smiled back. “I know that, of course. There is no doubt in my mind! I was upset, yes, but only because I could not share with you the lunch I made with Grillby! Undyne even helped; you would have enjoyed it, Sans. It was delicious!”

  
“Oh, I’m sure. I’ll make sure to be there next time; wouldn’t want to miss out on a good lunch with you and the Grillmaster.”


	4. Explosion

**Summary for the Chapter:**

> Shit finally happens.

Papyrus was the first to the door when he heard the bell ring, though Sans was close behind him. It wasn’t until Grillby actually came through it that Gaster showed up, hovering behind the two with a rare warm smile on his lips.

“Grillby!” Papyrus exclaimed, immediately latching onto the man; “I must show you something! It is in my room, and very important! I cannot tell you now, because it is a surprise! A wonderful surprise!”

Grillby returned his hug and chuckled, nodding his compliance. Sans grinned from behind his brother, happy, but not quite as enthusiastic.

“Hey, Grillby.”

He liked it when Grillby came over; he brought an air of warmth, and tended to be a peacebringer. Things were never wrong when Grillby was there.

Grillby beckoned Sans close and scooped him into the hug with his brother, which Sans enjoyed without showing it too much. When the three broke apart and Papyrus raced up the stairs to begin preparing whatever it was he had to show Grillby, the flame-headed monster moved over to Gaster. He took his hands for a moment, smoothing his thumbs over the back of them, and then leaned in to give him a quick kiss. Gaster appeared happy to receive the affection, but didn’t push back with any of his own.

Sans watched as the two left the house, and circled around back to the Lab. He could see their hands flicking through a silent conversation, but it was too quick and too close to their bodies for Sans to understand the words.

For a while, Sans entertained himself in the living room. There were plenty of things to do; every available surface had something interesting on it, some strange and mysterious amalgamation of various parts and scraps his father was in the process of either putting together or taking apart. They were thinking tools for Gaster, ways to entertain his hands so his mind was free to work, but for Sans, they were toys that brought him closer to his dad. And not just that, but they were the only toys he was interested in that weren’t tucked away in the nooks and crannies of his room; Papyrus had action figures, books, puzzle toys, and board games scattered around his room, all given to him by Grillby. But Sans had fewer tangible interests, and his room mostly just held a few books, journals, and the odd stuffed thing. Neither were allowed to keep things anywhere around the house, as Gaster judged them useless and distracting.

After a few long, quiet minutes in the living room, Sans put down the strange thing he’d been fiddling with and headed off to the Lab. He was bored, and he longed for the company of his father and Grillby.

Usually, Gaster and Grillby were warm and affectionate with each other. Grillby was a kind person, and he knew how to push Gaster just enough that the man responded well to his affections, received them, and on rare occasions, returned them. The gentle and persistent way in which Grillby handled Gaster kept him calm, happy, and easy. Sans had never seen them upset around each other.

Now was the exception; Gaster stood by The Machine, tense, braced as if for a physical fight. Sans wasn’t sure if he’d ever seen his father so close to The Machine without showing an inclination to work on it, but now Gaster’s full attention was focused on Grillby, and it was terrifying. His eyes seemed brighter, his features tight and contorted, and all of the energy he possessed seemed to be condensed and narrowed on Grillby, on being angry at Grillby. His hands worked in huge, jerky movements; “I know what I am doing. I know the science and the theories better than you _ever_ will.”

Grillby stood with his back to the door, to Sans. The air around him felt hot, even suffocating, but Grillby appeared a little more relaxed. He was clearly upset, but his stance portrayed a frustrated attempt to reason in comparison to Gaster’s defensive and rage-filled demeanor. “This will kill you, Gaster. You, Asgore, and it’ll put the rest of the Underground in danger!”

_"If I’m wrong!_ I have spent eleven years researching this, I have _raised_ my experiments-”

“‘Raised’ may be a strong word in this particular situation.” Grillby snapped.

_“I have done my best!”_ If hands could roar, Gaster was roaring.

“Your best hasn’t been enough, and you know it. Now you think it’s a fine idea to shove a human soul inside yourself and jeopardize your life- and mind you, Gaster, this isn’t just _your_ life. Your sons-”

“My sons are fine! They are capable, resourceful, and I have ensured success regardless. I know what I’m doing!”

“And if you fail?”

  
  
“You are not listening, I won’t-”

“You _could!_ If you cared about anyone around you, that would be enough.”  
  


Gaster fell silent for a moment, his stance wavering. Sans watched him, peeking out from behind Grillby. He still stood in the doorway. He was too afraid to move inside, to come into the fury-filled room; among other things, he wasn’t entirely sure he would survive such close proximity to Grillby’s intense heat. As the two argued, his thoughts began to buzz.

“I care, Grillby, but if I do not do this, they will live their lives underground. Trapped! Sans deserves more, and he knows he deserves more. If not, he will discover it soon. He has abilities.”

“Sans has a heart. He has a soul. He has a need for the affection and attention of a father, before anything else.”

“Sans will thank me-”

_“STOP!”_ Sans screamed the word with every fiber of his being, and the two men fell silent. His eyes were closed, leaking tears, and his body shook with the effort of holding himself together against the jagged thoughts crashing about inside him. “Stop, stop, shut up, just stop. Stop talking, stop _arguing,_ stop… talking about me, and stop talking about dying.”

Grillby went limp, losing his anger. He turned to Sans with compassionate eyes, and spoke verbally; “Sans, I’m-”

But Sans cut him off; “Shut up! I don’t care, just shut up.”

“Sans?” Papyrus was running to his brother, his voice loud and wavering with worry. Sans turned to look at him, and all but collapsed in his arms just as Papyrus reached him. The two sank to the floor.

Gaster did not react well. His anger had not subsided with the temporary shock of Sans’s outburst, and now it was spreading further than Grillby, directing itself to his sons as well. To Papyrus.

“Get out.” He strode slowly to Papyrus, his movements and his words low and dangerous. “You are now allowed in this place, and you will leave it immediately.” Grillby placed a hand on Gaster’s chest, establishing himself as a barrier between him and the boys. Gaster kept talking, and Papyrus watched him silently from the floor. Slowly, Sans raised his head to look at Gaster as well. “You do not possess the ability to understand any of this. You cannot see these things, and you are not capable of handling what is here. I’ve told you this, Papyrus. You know this. Get out.”

Papyrus didn’t respond. Gaster pushed Grillby aside, took a step closer.

“Stop. Leave us alone.” Sans’s voice was quiet, but more firm and confident than Gaster had ever heard it. It gave him momentary pause, but he seemed more angered by it than inclined to listen. He took another step. “Stop.” Sans’s pupils grew dim, and disappeared.

That stopped Gaster.

“Sans, your brother needs to leave. You both need to leave.”

A spot of blue began to glow in Sans’s left socket, and Gaster’s eyes widened. He took another step forward, stood over the two, appearing more concerned now than angry.

“Sans-”

**  
**The blue burned, smoked, and exploded.


	5. What Needs Saying

Papyrus laid on the ground in a heap, eyes dim, bones cold. He wasn’t dust, but he wasn’t moving, either.

Grillby was in a similar state; his flames small and lukewarm, his body limp and unresponsive. He seemed to twitch every now and then, though, as if he was just beginning to stir.

Gaster was wide awake, sockets alert, round, and fixed on Sans. He was pressed against the wall opposite his son, at least a foot off the ground. As Sans got to his feet, Gaster seemed to shift; he was moving sideways along the wall in small increments, like a magnet with the wrong side facing Sans.

Sans’s eyes still glowed blue, and remained fixated on Gaster. The man hadn’t been afraid many times before, and not ever at the fault of his sons. Now, though… The stare Sans gave him was intense, filled with a destructive emotion kept in check only by the background worry Sans had for his brother. If not for Papyrus’s presence, Gaster wasn’t sure he would be solid.

The sound of shifting cloth yanked Sans’s attention away from Gaster, and the man fell to the floor. As Sans turned to his brother, Gaster took the opportunity to all but run from the Lab.

It didn’t take long for Papyrus’s emotional state to become apparent; he was shaking, and even as he just began to wake again, fear took him over. He couldn’t seem to get his feet under him, but scraped them fruitlessly against the floor in a frantic attempt to push himself away from the source of the explosion. His voice was high-pitched and hysterical, but couldn’t seem to form any words; instead he made fearful sounds as he scrabbled to get away. Sans reached forward in an attempt to offer him some kind of physical comfort, but Papyrus’s eyes fixated on the still-glowing eye, and he finally found the traction to stand. He stumbled toward Grillby, seeking safety and solace. It took Sans a moment to register the fact that Papyrus was afraid _of him._

 

When it was clear that Sans wasn’t going to be able to help his brother calm down, he left.

Sans found Gaster back in his room. He was at his desk, working on some fine detail of the Machine’s blueprints, and his back faced the door. As Sans approached the doorway, he took a moment to calm himself, and the glowing blue that had shown the world his uncontrollable, impulsive anger, gave way to the usual steady white glow.

“I don’t really expect you to have a good reason for anything you’ve done.” Sans told him, and Gaster looked up, met his eyes. “You think you know what I want, and you think you know what Papyrus can handle, and you don’t. You don’t really pay enough attention to that stuff to know anything about it, and whatever. You’re busy. The Machine is more important, I get it.” He took a deep, shaky breath, suddenly feeling… thin. Intangible. Still, he felt more sure of himself than he’d ever felt before. “But you hurt us both, and I think Grillby’s right. Whatever you’re… doing, whatever it is, it’s going to make it worse. I can handle it, and Papyrus is strong, but he doesn’t deserve it." He swallowed around a hard lump. "Dad, he doesn’t deserve it.”

Gaster stood and faced him, though he kept his distance. His hands shook and his fingers flickered, trying to decide what words to shape. Than he found them; “I’m sorry.”

Sans watched, his expression filled with a melancholy hope.

“But Sans, look at you. You are… powerful.” As Gaster spoke, Sans’s fingers clenched in the hem on his jacket, and his eyes began to dim again. “You are a feat of science. You are different, but an incredible success. You are capable of things this world has never seen.” Sans’s pupils disappeared. “The Machine I am working on is an extension of what made you what you are. You contain a piece of a human soul, clinging to your bones, but absorbing now into the piece of myself I put into those bones. That is what makes you so extraordinary, Sans. And now… humans and monsters can join, but not perfectly. You know that, you have heard the legends. This machine could strip the souls of their agency and allow for a perfect union, a perfect being.” Gaster’s face was glowing with excitement, with the joy of sharing something incredible. Something _he_ had created.

“Does that mean Papyrus is a failure?” Sans’s tone was quiet again, dangerous. Gaster’s excitement wavered.

“He is, but-”

“Then you have no idea what you’re talking about.”


	6. Work

Gaster didn’t improve. He didn’t change. It seemed that every word Sans had spoken to him went through him, like he wasn’t even there. The only information he retained was that Sans was dangerous to him; more than he’d thought. He withdrew into himself, into his Lab, and worked harder on his Machine than he had ever worked before. He prepared for another explosion, and tried to make himself strong; not just more than himself, but more than Sans.

 

Sans was left alone.It wasn’t entirely anyone else’s fault; Papyrus spent most of his time with Grillby, still cautious around his brother, but it was Sans who avoided them. It was Sans who avoided subjecting them both to the fear and danger his presence seemed to bring. His mind dragged him down into a pit, and he was unwilling to let anyone else know for fear of dragging them into it with him. Instead, he kept himself alone. He thought, felt, analyzed, and despaired; all in silence. He didn’t trust himself enough to seek the support he needed.

 

When Sans woke one night screaming, he felt more alone than he ever had before. His first instinct was to find Papyrus, but his mind shut down the idea so quickly it burned. He felt small, isolated, his room cold and eerie with the glow of a burning blue eye. His breath seemed to shiver, and his muscles were so tense and tight that he shook. Sans closed his sockets, shut the light inside himself, and tried to calm himself with the vice-like grip of tiny, boney hands around his upper arms.

 

When he opened his eyes again, no less a hysterical mess, Papyrus stood in his doorway, watching with a mixture of pity and fear. His sockets were fixated on Sans’s glowing blue eye, and he looked… frozen. Sans understood; the blue pupil was a source of fear now for Papyrus. It meant Sans was unstable and out of control, and it meant he could do something dangerous again. He couldn’t help Sans so long as it glowed. So Sans took a breath, then another, tried to calm himself on his own so that Papyrus wouldn’t be afraid anymore. After a moment, The blue faded, and his pupils returned to normal. Papyrus seemed to relax, and started to walk toward him.

 

But the emotions returned, rushed to the surface again, and Sans curled in on himself and began to shake and cry as he had before. “Sorry,” he managed, his voice a whisper between broken breaths, “I can’t stop it, I’m sorry.” His fingers tightened around his arms again, squeezing, pinching, trying and failing to stop the flood of emotions. Papyrus sat on the bed, cautious, and couldn’t bring himself to do much more. Sans went on, “I’m supposed to protect you, but I didn’t. I hurt you when I was trying to stop Dad, and I’m really sorry, Paps. I’m really sorry. I’m trying to stop, but I can’t, I’m out of control and I’m powerful and different and dangerous, Dad said so, what do I do about that? I’m sorry, I’m sorry, I hate this, I hate this, I hate this, I hate this…” He rocked himself, mumbling the same words over and over like a panicked mantra.

 

Papyrus took one of the hands from around his arm and pulled it away, squeezing it in his own.

  
“It is okay, Sans.” He said, just loud enough for Sans to hear him over his stream of fearful mumbles. “I am working on my fear as well.” He covered their little bundle of hands with his other hand, and when Sans met his eyes, Papyrus held them. “It is okay.”


	7. Exposition

Gaster had always been thorough; he ran experiments regularly in order to check and re-check the Machine, the progress he had made, the actual causes and effects of whatever he was creating. It was simply good science, and a necessary part of the process. But he had never been able to test it on anything alive; instead, he used the Machine on  samples of Monster Dust donated to Royal Science by the citizens of the Underground, of which there was plenty. Still, the sounds of the Machine only permeated their house a few times every couple of weeks. They were infrequent, and a sign of routine maintenance on Gaster’s project. They started, and lasted only until Gaster found a flaw. Then they stopped.

 

Now, though, the sounds were nearly constant. The grinding, whirring, and humming broke the regular silence of the house without ever seeming to cease. It was clear that something had happened with the Machine; Gaster couldn’t find any new flaws, any bugs to iron out, anything. Either he was stuck, or it was done.

 

But only so much could be gleaned from experiments ran on simple clumps of dust, when the real thing was to be used on living monsters.

 

* * *

 

 

Through the blissful darkness of Sans’s sleeping consciousness came a sense of uncertainty, a lack of safety and peace. It lingered as steadily as a notion can in a dream, then grew stronger, and more… until Sans found himself stirring from his rest in the middle of the night. His eyes opened on the ceiling, but there was something else…

 

Gaster. His dad stood above him, hand outstretched as if to rouse Sans, but it was still. He’d been standing there a long time, seemingly incapable of actually waking him. 

 

“How long have you been standing there?” Sans mumbled, groggy and disoriented, but quickly coming awake.

 

Gaster didn’t respond, instead retracting the hand and motioning for Sans to come with him. 

 

They moved to the Lab, which looked… austere. Aside from the Machine and a countertop full of blueprints, everything had been put away. It was all clear, it was… ready. 

 

Gaster, appearing nervous and somewhat antsy, took a moment to organize the mess of blueprints. Sans watched him from the other side of the room, his eyes wide and analytical. Everything seemed so strange, so different from the normal state of things. The Lab wasn’t supposed to be clean, and the Machine wasn’t supposed to be tested so often, and Gaster _never_ woke him like this, and when was the last time he had seen his father _nervous?_   

 

Something was going on. Something was wrong.

 

After a long moment, Gaster turned to Sans and began to move his hands into quick, impulsive words. His eyes flicked about, incapable of focusing on any one thing. 

 

“I created you and your brother from the discarded bones of humans, fused with pieces of my soul. Both of you I fused with a piece of a human soul, but in two different ways. Your’s succeeded, your brother’s did not. He failed; but you are better, special, capable of incredible feats of magic and intuition that no other monster can achieve with such rudimentary physical compositions.” Gaster was beginning to beam, but the repetition of that ostracizing narrative made Sans shiver. 

 

“That was the first experiment; the one that told me such a perfect fusion was possible. Normally, the human soul resists and retains some agency, but your monster soul absorbed the human fragment so perfectly, so flawlessly… over time it improves, and so does your power. That is the union we need Asgore to achieve in order to save us all. That is the union that will fix our problems and bring us back to the world we deserve.

 

“The humans have stolen this planet. They are afraid of our ability to take their souls, but remain ignorant to the fact that this ability is imperfect. If Asgore were to take all seven human souls and find that they resist so that he is incapable of breaking the barrier, thousands of years of struggling will be for nothing. We cannot spend another thousand years in this place, Sans. I will not allow you to be confined to a world without a sky.

 

“The Machine amplifies our ability to consume a human soul, and subdues the part of the human soul that resists consumption. Nothing likes to be forced, but by removing the sentience of the soul and extracting the DETERMINATION, the Machine can make something alive and willful nothing more than power for the taking. The Machine contains that power here, you see-” Gaster was just moving to start explaining the pieces of the Machine in detail when Sans stopped him.

 

“Why are you telling me this?”

 

Gaster stopped what he was doing, and turned a steady, still-fearful smile on his son. 

 

“I have nearly finished the Machine. Every experiment has yielded the same results; there is nothing left to fix; nothing that such small experiments will tell me. The next step is to test this on a living monster.”

 

Sans’ eyes widened. “Dad-”

  
“I would not experiment on another monster, Sans.” Gaster interrupted, “This I will try on myself.” 


	8. Chapter 8

Sans remembered the argument Gaster and Grillby had had no more than a week ago, the one about Gaster doing something dangerous to himself, but he hadn’t fully realized what the implication of either’s words were; they hadn’t sunk in. Now, though, he understood. He understood what his father planned to do, and what that could mean, and above all, he understood how _dangerous_ that was. He understood what he could lose.

 

Gaster wasn’t the best father, and he knew that. He saw him in stark contrast to Grillby on a regular basis, and he could analyze and pick apart each and every way in which Gaster failed to be even as good as a flame monster with questionable relations to the family. But he was Sans’s dad anyway. As justified as he would have been in hating and condemning the man, he couldn’t. He couldn’t bring himself to throw away the little scraps of positivity he _did_  have, the occasional good moments and glimpses of something warm inside his father, something nice that was just _almost_  there, almost close enough to the surface to mean something.

 

And now Gaster was making that decision for him, making the decision to throw his life away for an experiment. 

 

“I may not live, Sans.” The man confirmed, now talking far more slowly and carefully, almost pleading with his son. “I must do this, but I may not come out alive. I want you to know everything, every detail of why this is important and how my Machine works. I want you to recreate it and carry on my work. I want you to understand.”

 

“You… you can’t die.” Sans had to work to form the words; his mouth felt too dry. “You aren’t going to die. You won’t do this, because you can’t.”

 

“Sans, I have to. I explained this, that is why I explained, I-”

 

“No, you don’t! Monsters can already take human souls, you don’t need to make that _better,_  and what if humans find out? That won’t help!”

 

“They may try to kill us regardless, and if Asgore isn’t capable of containing the souls to break the barrier, Sans, we need to be strong like you are, capable like you are, we need-”

 

_"No one_  should feel like I do.”

 

“You were just a test run, Sans, and even then you are so perfect, so much better than the others. You are incredible, Sans, and you should take pride in that. Take pride in how much better off you are than everyone else.”

 

Sans clenched his fists. His eyes went dark. “If you do this, I’m taking Papyrus to Grillby's.”

 

“I have to, Sans, listen-”

 

Sans left.

 

__________

 

Papyrus was sleepy and confused, but he understood the urgency in Sans’s tone as he pried his brother from his bed. Sans seemed distraught, on the verge of another emotional explosion, but was soothed by Papyrus’s compliance and steady reassurance. The two took a moment to pack a few belongings, and left the house together. 

 

The door had barely closed when the screaming began. 

 

From the back of the house, from where the Lab was, the whirring and clicking and grinding of the Machine mixed with an unearthly, pain-filled shrieking. 

 

Neither brother had heard their father do more than hum before, but they recognized the sound of his voice. 

  
As Sans stopped, bones filling with a cold, sharp panic, Papyrus let go of his hand and ran inside.


	9. Slip Away

Sans was frozen for a moment, incapacitated by the realizations trying to force themselves through a shell of numbness. The coldness was there, but the sharpness of his fear had faded, and he was left with something thicker and more suffocating. He realized he wasn’t breathing, and tried to push air through-- he wasn’t sure what. He was a skeleton and a monster, he wasn’t sure why he did anything. Maybe the spacial nature of his magic, or a physical manifestation of his soul, or… The train of thought dropped off, and Sans lost the will to hold onto it. It was simple and easy, but another scream rang through the house, through the air, and vibrated deep in his bones. Sans allowed simplicity to slip away, and found himself whirling through the cracks in space.

 

He arrived in the Lab, where Papyrus was too busy trying to extract his father from the Machine to be surprised by Sans’s teleportation. Sans saw the danger in his actions immediately, and with the push of another of Gaster’s soul-twisting screams, Sans was glowing blue and yanking Papyrus away. 

 

Papyrus looked at him with vivid fear in his eyes, and Sans returned the look with one of absolute panic. His brother was in danger, and his dad was stuck in the Machine, bent inside it like the bowl part of a mixer with wires stuck to just about every square inch of available skin. Gaster’s features were distorted with pain, but he did nothing to stop it. The screams that continued to burst forth from him were nothing short of terrifying. One of the few sounds Sans had ever heard his father make, and it was one of intense, repeated suffering; stabbing through Sans and freezing him, squeezing him, twisting him. He couldn’t think past getting Papyrus away from the Machine, from Gaster, from the source of everything terrible in this moment. And after he did that, he was frozen. Purposeless. What else could he do? His mind was whirring and buzzing and spinning, but it was too fast to latch onto anything; and with no clear action to push for, Sans was trapped.

 

And all at once, everything stopped. 

 

The sudden silence was almost louder than the shrieking had been. 

 

Gaster stared straight ahead, eyes empty, seeming to… glow, sort of, a steady neon purple. 

 

He turned to look at Sans, who was watching him in shock. Time had stopped, and Sans could feel it. Papyrus wasn’t moving, the room was quiet, and even the air had ceased to move. Gaster sighed, and for a moment, Sans watched him turn to dust, as if the pieces of him had lost the will to hold together. They stayed in the same shape, though, refusing to fall to the floor… and then they came together again, and Gaster was solid. 

 

He slumped in the Machine’s chair, and as his consciousness fled, his hold on time followed. 

  
Sans didn’t take a second to think. When he saw that Papyrus was moving and alive, he slipped through space to Grillby’s.

**Author's Note:**

> Please let me know if you have any criticisms, suggestions, or ideas! I really love hearing from you guys.
> 
> Also, if you have any unusual triggers and you plan on following this story, let me know. I'll add it in a note at the top so you can navigate this fic safely.


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